Adhesive sacrificial bonding of spatial light modulators

ABSTRACT

A method of combining components to form an integrated device, wherein at least one first component is provided on a first surface of a sacrificial substrate, and at least one second component is provided on a first surface of a non-sacrificial substrate. At least one support structure is formed on at least one of the first surfaces of the sacrificial substrate, and the non-sacrificial substrate, respectively, such that said at least one support structure is extended outwardly from at least one of the first surfaces. The sacrificial substrate carrying the first component, and the non-sacrificial substrate carrying the second component, respectively, are bonded, so that the first and second surfaces will be facing one another with a distance defined by a thickness of the support structure. At least a part of the sacrificial substrate is removed. The first component and second components are interconnected.

TECHNICAL FIELD

The present invention relates in general to techniques for forming anintegrated device, e.g. a semiconductor device, and in particular to amethod for integrating micro mirrors on an integrated circuit.

DESCRIPTION OF THE BACKGROUND ART

It is well known in the current art to build spatial light modulators(SLM) of a micro mirror type, e.g. U.S. Pat. No. 4,566,935, U.S. Pat.No. 4,710,732, U.S. Pat. No. 4,956,619. In general two main principlesfor building integrated devices, such as micro mirror SLM, have beenemployed.

An integrated circuit (IC) is manufactured to a finished state, and thenthe micro mirrors are manufactured on said IC. The micro mirrors arebuilt onto the IC wafers. An advantage with this approach is that socalled IC foundries can be used, which present a very cost efficientmanufacturing of the electronics wafers. A disadvantage is that there isa very restricted selection of materials and methods that are usable forthe manufacturing of the micro mirrors, because there is an uppertemperature limit of about 400° C., above which the electronics will bedamaged. This makes the manufacturing of micro mirrors having optimalperformance more difficult.

Another way of building micro mirror SLM's is at the end of the processfor making the IC, and micro mirror manufacture is started on the samewafers. The advantage with this approach is that there is a greaterfreedom of selecting materials, methods and temperatures for themanufacture of micro mirrors having good performance. A disadvantage isthat the IC wafers cannot be manufactured in standard IC foundries. Thisis because IC wafers are subject to very strict demands on the processof manufacturing in terms of standardization in order to be able tomaintain the quality in the process.

Therefore, there is a need in the art for an improved method formanufacturing micro electric/mechanical/optical integrated devices.

SUMMARY OF THE INVENTION

In view of the foregoing background, the method for manufacturingintegrated devices, such as for example micro mirror SLM's, is criticalfor the performance of such devices.

Accordingly, it is an object of the present invention to provide animproved manufacturing method for an integrated device which overcomesor at least reduces the above mentioned problems.

In a first embodiment, the invention provides a method of combiningcomponents to form an integrated device, wherein at least one firstcomponent is provided on a first surface of a sacrificial substrate, andat least one second component is provided on a first surface of anon-sacrificial substrate. At least one support structure is formed onat least one of said first surfaces of said sacrificial substrate, andsaid non-sacrificial substrate, respectively, such that said at leastone support structure is extended outwardly from at least one of saidfirst surfaces. The sacrificial substrate carrying said at least onefirst component, and said non-sacrificial substrate carrying said atleast one second component, respectively, are bonded with a temporarilyintermediate bonding material, so that said first and second surfaceswill be facing one another with a distance defined by a thickness ofsaid support structure. At least a part of said sacrificial substrate isremoved. Said at least one first component and said at least one secondcomponent are then interconnected.

In another embodiment, the invention further comprises the action ofpatterning said at least one first component after bonding saidsacrificial substrate with said non-sacrificial substrate.

In yet another embodiment, the invention further comprises the action ofarranging a metal layer on a first surface of said at least one firstcomponent facing away said non-sacrificial substrate after said bonding.

In still anther embodiment, the invention further comprises the actionof arranging a metal layer on a second surface of said at least onefirst component facing said non-sacrificial substrate prior to saidbonding.

In another of the invention embodiment, said metal layers on said firstand second surfaces of said first component are of equivalent thickness.

In anther embodiment, the invention further comprises the action ofperforming said interconnection of said at least one second componentwith said at least one first component with the help of said at leastone support structure.

In another embodiment, the invention further comprises the action ofsecuring said at least one first component to said non-sacrificialsubstrate with means other than said temporarily intermediate bondingmaterial.

In another embodiment, the invention further comprises the action ofstripping away said intermediate bonding material.

In another embodiment of the invention said support structure is made ofelectrically non-conducting material.

In another embodiment of the invention said support structure is made ofelectrically non-conducting material.

In another embodiment, the invention further comprises the action ofdepositing an electrically conducting material on at least a portion ofa surface of said support structure, prior to said bonding, for formingan electrical connection between said at least one first component andsaid at least one second component.

In another embodiment, the invention further comprises the action ofperforming said securing of said at least one first component to saidnon-sacrificial surface and said interconnection of said at least onefirst component with said at least one second component in a singleaction.

In another embodiment of the invention said first component and saidnon-sacrificial surface are secured to each other by one of the group ofevaporation, spin coating, sputtering, plating, riveting, solderinggluing.

In anther embodiment of the invention said intermediate bonding materialis a low temperature adhesive, e.g., an organic material like athermostat polymer, polyimide, benzocyclobutene (BCB), epoxy,photoresist. The intermediate bonding material can also be an inorganicmaterial.

In another embodiment of the invention said first component is a micromirror.

In another embodiment of the invention said first component is made ofsingle crystalline silicon.

In another embodiment of the invention said second component is anintegrated circuit.

In another inventive embodiment of the invention said integrated deviceis a micro mirror Spatial Light Modulator (SLM).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a first process step according to an embodiment of theinvention.

FIG. 2 shows a second process step according to an embodiment of theinvention.

FIG. 3 shows a third process step according to an embodiment of theinvention.

FIG. 4 shows a fourth process step according to an embodiment of theinvention.

FIG. 5 shows a fifth process step according to an embodiment of theinvention.

FIG. 6 shows a sixth process step according to an embodiment of theinvention.

FIG. 7 a illustrates schematically a top view of a portion of a micromirror SLM.

FIG. 7 b illustrates schematically a side view of a portion of a micromirror SLM shown in FIG. 7 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purpose of this application, the terms “wafer” and “substrate”are used interchangeably, the difference between them merely amountingto dimensions thereof.

“Component” shall be taken to mean any structure that is provided as asubunit on a wafer or substrate, and can comprise entire devices, aswell as details of such devices, even a single piece of a material.

The method according to the present invention is particularly suited forthe manufacturing of micro mirror Spatial Light Modulators. However, itwould be applicable to a wide variety of thermal and non thermaldetector devices, such as, but not limited to, quantum well detectors,pyroelectric detectors, bolometers, etc. It is particularly suitablewhen for some reason it is not possible to process/pattern/deposit astructure (e.g. a micro mirror array) directly on a substrate, whereanother structure (e.g. steering electronics) is present. This can e.g.be the case if the structure provided on said substrate is temperaturesensitive to the process temperature for the processing of the structureto be provided thereon, or when the substrate is polycrystalline and theelements that are grown on top of the substrate must bemenochrystalline.

FIG. 1 illustrates schematically a first process step according to anembodiment of the invention. Thereby a first wafer 200, in the followingreferred to as a non-sacrificial substrate, having control electronics(and/or other types of circuitry), is manufactured by some standard typeand cost efficient process, such as those methods commonly employed inApplication Specific Integrated circuit (ASIC) production, or in “IC”foundries.

On these non-sacrificial substrates there can for example be providedelectrodes 210 and support structures 220, by means of which a device ordevices 120 (e.g. micro mirror or some other type of component forexample an electric/mechanical/optical component), provided on a secondwafer 100, in the following referred to as a sacrificial substrate, andto be integrated with the pre-made non-sacrificial substrate 200 are tobe attached to said non-sacrificial substrate 200. The sacrificialsubstrate 100 may for instance be made of some semi-conducting materiale.g. silicon. Between said sacrificial substrate 100 and said device orcomponent 120 there is preferably arranged an etch stop layer made offor instance SiO2 110.

The component or components 120 is/are manufactured on one side of saidsacrificial substrate 100, preferably made of silicon and mostpreferably single crystalline silicon, although other materials arepossible, e.g. AlGaAs, glass, quartz, InP, Sic, SiN etc. Materials andprocesses for each wafer are selected for the best possible performanceof each part (selectively, response times, life span requirements etc.).

In FIG. 1 the support structure 220 is arranged on said non-sacrificialsubstrate 200. By arranging said support structure 220 on thenon-sacrificial substrate 200, the sacrificial substrate does not haveto be aligned to the non-sacrificial substrate. However, it is possibleto arrange the support structures 220 on said sacrificial substrate 100,i.e. on said component material 120; or on both the sacrificialsubstrate 100 and the non-sacrificial substrate 200, but then thesacrificial substrate 100 and the non-sacrificial substrate 200 have tobe aligned.

The sacrificial wafer 100 may, as shown in FIG. 1, be coated with anuncured polymer layer 130. A suitable polymer is epoxy, although othermaterials are possible too, for example, BCB (benzocylobutene), anyphotoesist, any polyimide, any thermostat materials or any organic orinorganic adhesive material in general on top of said component orcomponents 120.

However, said non-sacrificial substrate 200 may be coated with saiduncured polymer layer 130 (not shown), either instead of coating saidsacrificial substrate 100 or in addition to coating said sacrificialsubstrate 100. There might be different coatings on one or on bothsubstrates 100, 200.

The sacrificial substrate 100 and the non-sacrificial substrate 200 maybe brought together under pressure or without pressure and preferablyalso with healing, FIG. 2. Before they are brought together saidadhesive material may be procured at 60° C. for about 5 min. Thus, thesacrificial substrate 100 and the non-sacrificial substrate 200 will betemporarily bonded together by the polymer layer 130, that functions asan adhesive material. This procedure can be performed with standardequipment. For example, the two wafers may be bonded together with abonding pressure of about 1 bar in a vacuum. While applying the pressurethe temperature of the wafer is ramped up to for example 200° C. for twohours to cure the adhesive material. The applied pressure is high enoughso that the support structure 220 arranged on the non-sacrificialsubstrate 200 will contact the components 120 arranged on saidsacrificial substrate 100.

When, as shown in FIG. 1, the adhesive material 130 is arranged on thesacrificial substrate one cannot completely remove all adhesive materialbetween the support structure 220 and the component 120 if the free topsurface of said support structure facing said adhesive material iscompletely flat. However, by forming said top surface of said supportstructure like a curved surface or the like, such effect can beeliminated or at least reduced to a significant degree.

The component 120 may be covered by at least one metallization layer orlayer of another material (not shown) facing said non-sacrificialsubstrate 200.

When said adhesive material is arranged on said non-sacrificialsubstrate 200, said adhesive material can be removed from said top freesurface of said support structure 220 prior to said bonding step.Preferably said adhesive material 130 is removed by lithographicalmethods, lapping or polishing. The adhesive material 130 may forinstance be applied to said non-sacrificial substrate 200; to saidsacrificial substrate 100; or to both said non-sacrificial substrate 200and said sacrificial substrate 100, by spinning, i.e. rotating thesubstrate while applying the adhesive material. When removing theadhesive material 130 from the top free surface of the support structureby means of lithography methods some adhesive material in areas aroundsaid support structure 220 may also be removed. In the same way, if theadhesive material is applied on the sacrificial substrate 100, theadhesive material may be patterned with lithographical methods in orderto create space for the support structure 220. Said space may be biggerthan necessary or essentially the same size as the support structure.The patterning of the adhesive layer takes place before bonding thesacrificial substrate 100 to the non-sacrificial substrate 200.

By choosing a predetermined thickness of said support structure 220 andarranged one or a plurality of them on either substrate 100 or 200 thedistance between the sacrificial substrate 100 and the non-sacrificialsubstrate 200 can be controlled. The distance between thenon-sacrificial substrate 200 and the surface of the component 120facing the non-sacrificial substrate 200 will essentially be thethickness of the support structure. It may vary a little due to the factthat some intermediate bonding material will still be left between thetop of the support structure.

The sacrificial substrate 100 may partly or wholly be etched away, FIG.3, or removed in some other way, such that for example only the actualcomponent remains. This can be done by wet etching, e.g. by using KOH,EDP, TMAH or grinding/polishing, just to mention a few possibilities,and the skilled man will find suitable techniques using his ordinaryknowledge. Dry etching of e.g. RIE type can also be used. Said etch stoplayer 110 may be needed on the semi-conducting sacrificial substrate,e.g. silicon, such that the etch will not be brought in contact with theadhesive material or the surface of the non-sacrificial substrate 200.

Etch stop layers may be removed by dry or wet etching. Etch step layersmay be of Silicon dioxide; Silicon Nitride; or a suitable metal or otherinorganic or organic material.

Thereafter an optional metallization step is performed. If the opticalproperties of the material used in the component or components 120 isnot good enough another material with better optical characteristics canbe arranged on said free surface of said component or components 120.The arrangement of said material may for instance be performed by usingsputtering, plating, Chemical Vapor Deposition, or similar methods wellknown for a man skilled in the art. A material with good opticalcharacteristics is aluminum, at least from the point of view ofreflectivity.

In order to form a pattern on the component 120 a layer of photoresist150 is spun on top of the free component surface either covered with ametallization layer 140 or not. By using well-known techniques ofphotolithography a desired pattern may be arranged in said layer ofphotoresist. By using an etching agent recommended for the usedphotoresist a well characterized pattern can be accomplished in saidcomponent material.

The pattern may for instance by the micro mirror array, a part of which400 is shown in FIG. 7 a, which is characterized by individually movablereflecting elements 170, see FIGS. 7 a and 7 b. Attached to said mirrorelements are torsion or flexible elements 180 in the form of hinges.When applying a first voltage on the electrode 220 and a second voltageon the reflecting element 170 the potential difference will create aelectrostatical attraction force which will bend/move the reflectingelement in a desired way.

In a next step the patterned component 120 may be interconnected withthe non-sacrificial substrate by means of depositing a connectingmaterial e.g. by sputtering, electroplating, evaporation, chemicalvapour deposition or a similar deposition technology. Saidinterconnection can be performed with the help of the support structures220, see FIG. 5. If the support structures 220 are made of electricallyconducting material, or coated partly with an electrically conductingmaterial, and the component material above said support structure isprovided with a hole, said connecting material deposition can be done byplating, sputtering, evaporation or any other deposition technology.

Instead of metal riveting the support structure may be provided with ahollow space, for example U-shaped, in which for example the adhesiveagent (a glue, photo resist or something similar) may be found. Theadhesive agent physically connects the patterned component 120 with thesupport structure 220. In this embodiment the adhesive agent is enclosedin a volume defined by said hollow support structure and said patternedcomponent 120.

The support structures can therefore be considered to have twofunctions. A first function is the first described namely to provide thesacrificial substrate 100 and the non-sacrificial substrate 200 in apredetermined distance from each other given by the thickness of saidsupport structures. A second function would then be to assist in theinterconnection of the component 120 with the circuitry (which e.g.could be a CMOS integrated circuit) provided in the non-sacrificialsubstrate 200. When said support structure is not made of electricallyconducting material and said interconnection of said component 120 withsaid circuitry is meant to be electrical, said support structure has tobe provided with an electrically conducting coating. Electricallyconducting material can be deposited on at least a portion of thesurface of said support structure, prior to said bonding, for forming anelectrical connection between said component 120 and the circuitry inthe non-sacrificial substrate 200.

However, there may be support structures with only a supportingfunction, i.e. to define a specific distance between the sacrificialsubstrate and the non-sacrificial substrate after bonding.

As can be seen in FIG. 5, the metal rivet may extend outwardly from thesurface of the component. Said outwardly extending part may be removedby polishing, lapping or similar methods.

The metal rivet does not only form an electrical connection between saidcircuitry in said non-sacrificial substrate 200 and said component 120but also secures said component 120 to said support member. By havingsecured the component to said support member it is safe to remove thetemporary adhesive bonding material 130 by for example an appropriateetching agent.

The support structure may be made of the adhesive bonding material 130.The structures may be made by lithographical methods, where the supportstructures will be cured by electromagnetic radiation while theremaining adhesive bonding material stays in original form.

The outmost surface or the entire film, which may be of semiconductingmaterial, of the sacrificial substrate 100 facing the non-sacrificialsubstrate 200 may be doped. This doping makes the material electricallyconducting.

The component or components 120 may have a layered structure ofdifferent materials. This layered structure functions as a stresscompensation. One material may be silicon and the other material may bea metal or silicon nitride or silicon dioxide.

The elements which are to be arranged on the non-sacrificial substratemay partly or completely be pre-patterned on the sacrificial substrate.For example SLM micro mirrors may be formed on said sacrificialsubstrate prior to bonding said sacrificial substrate with saidnon-sacrificial substrate.

A Spatial Light Modulator according to an embodiment of the presentinvention has a plurality of modulating elements in the form of micromirrors 120. These micromirrors are made of a single crystallinematerial. Examples of suitable materials are single crystalline silicon,single crystalline germanium, single crystalline germanium, singlecrystalline gallium arsenide, single crystalline indium phosphide orsingle crystalline silicon carbide. There are support members 220 whichelectrically and/or mechanically interconnect said micromirrors to asubstrate 200 on which there is provided at least one integrated circuit(made by but not limited to for example CMOS, bi-CMOS, bi-polar, andsimilar processes). The support members essentially define the distancebetween the micromirror and said substrate.

The micro mirrors are preferably made of a high temperature annealedand/or high temperature deposited (single crystalline) material.

Thus, although there has been disclosed to this point particularembodiments of the method of combining components to form an integrateddevice, it is not intended that such specific references be consideredas limitations upon the scope of this invention except in-so-far as setforth in the following claims. Furthermore, having described theinvention in connection with certain specific embodiments thereof, it isto be understood that further modifications may suggest themselves tothose skilled in the art. The intention is to cover all suchmodifications to fall within the scope of the appended claims.

1. A method of combining components to form an integrated device, comprising the following steps: providing at least one first component on a first surface of a sacrificial substrate, providing at least one second component on a first surface of a non-sacrificial substrate; forming at least one support structure on at least one of said first surfaces of said sacrificial substrate, and said non-sacrificial substrate, respectively, such that said at least one support structure is extended outwardly from at least one of said first surfaces; bonding said sacrificial substrate carrying said at least one first component, and said non-sacrificial substrate carrying said at least one second component, respectively, with an intermediate bonding material, so that said first and second surfaces will be facing one another with a distance essentially defined by a thickness of said support structure, removing at least a part of said sacrificial substrate; mechanically and/or electrically interconnecting said at least one first component and said at least one second component.
 2. The method according to claim 1, further comprising the action of: patterning said at least one first component after bonding said sacrificial substrate with said non-sacrificial substrate.
 3. The method according to claim 1, further comprising the action of: arranging a metal layer on a first surface of said at least one first component facing away from said non-sacrificial substrate after said bonding.
 4. The method according to claim 3, further comprising the action of: arranging a metal layer on a second surface of said at least one first component facing said non-sacrificial substrate prior to said bonding.
 5. The method according to claim 1 comprising the action of: doping at least one first component made of semiconducting material and facing said non-sacrificial substrate prior to said bonding.
 6. The method according to claim 4, wherein said metal layers on said first and second surfaces of said first component are of equivalent thickness.
 7. The method according to claim 1, further comprising the action of: providing at least one additional layer of stress compensating material on said first component.
 8. The method according to claim 7, wherein said stress compensating material is at least one of the materials of: SiO2, SiN, metal.
 9. The method according to claim 1, further comprising the action of: performing said interconnection of said at least one second component with said at least one first component with the help of said at least one support structure.
 10. The method according to claim 1, further comprising the action of: securing said a least one first component to said non-sacrificial substrate with means other than said temporarily intermediate bonding material.
 11. The method according to claim 10, further comprising the action of: stripping away said intermediate bonding material.
 12. The method according to claim 1, wherein said support structure is made of electrically non conducting material.
 13. The method according to claim 1, wherein said support structure is made of electrically conducting material.
 14. The method according to claim 12, further comprising the action of: depositing an electrically conducting material on at least a portion of a surface of said support structure, prior to said bonding, for forming an electrical connection between said at least one first component and said at least one second component.
 15. The method according to claim 1, further comprising the action of: performing said securing of said at least one first component to said non-sacrificial surface and said interconnection of said at least one first component with said at least one second component in a single action.
 16. The method according to claim 1, wherein said first component and said non-sacrificial surface are secured to each other by one of the group of: evaporation, spin coating, sputtering, plating, riveting, soldering, gluing.
 17. The method according to claim 1, wherein said intermediate bonding material is a low temperature adhesive, e.g. a polymer selected from poly-imide, bensocyclobutene (BCB), epoxy, photoresist.
 18. The method according to claim 2, wherein said first component is a micro mirror.
 19. The method according to claim 1, wherein said first component is made of single crystalline material.
 20. The method according to claim 19, wherein said first component is made of single crystalline semiconducting material.
 21. The method according to claim 1, wherein said second component is an integrated circuit.
 22. The method according to claim 1, wherein said integrated device is a micro mirror Spatial Light Modulator (SLM).
 23. The method according to claim 1, wherein said support structure is hollow with an open end.
 24. The method according to claim 1, further comprising the action of: forming said support structure lithographically by patterning the intermediate bonding material prior to bonding.
 25. The method according to claim 1, wherein the component 120 is at least partly prefabricated prior to bonding.
 26. A Spatial Light Modulator having a plurality of micro mirror modulating elements, wherein said micromirrors are made of single crystalline material, and where support members electrically and/or mechanically interconnect said micromirrors to a substrate provided with at least one integrated circuit (made by but not limited to for example CMOS, bi-CMOS, bi-polar, and similar processes).
 27. A Spatial Light Modulator according to claim 26, wherein said support members essentially define the distance between the micromirror and said substrate.
 28. A Spatial Light Modulator having a plurality of micro mirror modulating elements, wherein said micro mirrors are made of high temperature annealed and/or high temperature deposited material, and where support members electrically and/or mechanically interconnect said micro mirrors to a substrate provided with at least one integrated circuit (made by but not limited to for example CMOS, bi-CMOS, bi-polar, and similar processes).
 29. A Spatial Light Modulator having a plurality of micro mirror modulating elements, wherein said micro mirrors are made of single crystalline silicon, and where support members electrically and/or mechanically interconnect said micro mirrors to a substrate provided with at least one integrated circuit (made by but not limited to for example CMOS, bi-CMOS, bi-polar, and similar processes).
 30. A Spatial Light Modulator having a plurality of micro mirror modulating elements, wherein said micro mirrors are made of single crystalline silicon germanium or single crystalline germanium or galium arsenide or indium phosphide or silicon carbide and where support members electrically and/or mechanically interconnect said micro mirrors to a substrate provided with at least one integrated circuit (made by but not limited to for example CMOS, bi-CMOS, bi-polar, and similar processes).
 31. The method according to claim 1, further comprising the action of: arranging a metal layer on a second surface of said at least one first component facing said non-sacrificial substrate prior to said bonding. 